The Islamic State group's leader in Afghanistan and Pakistan, Hafiz Saeed was killed in a US drone strike in Nangarhar province on July 26, Afghanistan's ambassador to Pakistan has told the Reuters news agency.

Hazrat Omar Zakhilwal, the top Afghan diplomat in Pakistan, said on Friday several senior commanders and fighters were also killed along with Saeed in the strike.

Saeed was the head of IS's "Khorasan province," including Afghanistan, Pakistan and parts of neighbouring countries.

The death of Hafiz Saeed is a major blow to Islamic State (ISIS) efforts to expand from Syria and Iraq into Afghanistan and Pakistan as a serious force.

Saeed's death is the second US killing of one of the most prominent militants in the region in recent months. In May, the Afghan Taliban leader Mullah Akhtar Mansour was killed in a US drone strike in Pakistan.

Pentagon deputy press secretary Gordon Trowbridge said the strike came while the special operations forces of both US and Afghan carried out counter-IS operations in southern Nangarhar province throughout July.

"During this time, US forces conducted an airstrike targeting Hafiz Saeed Khan, the Islamic State in the Levant-Khorasan emir, in Achin district, Nangarhar province July 26, resulting in his death," Trowbridge told AFP.

"Saeed was known to directly participate in attacks against US and coalition forces and the actions of his network terrorized Afghans, especially in Nangarhar," he added.

Saeed, who was a former member of the Pakistani branch of the Taliban, has been reported dead last year in another strike. But his death was never confirmed.